1. Field of the Invention
The present invention relates to a laminated body and a method for producing the same. More particularly, the present invention relates to a laminated body in which a part of the layers are in a sintered state and the contraction thereof due to baking is suppressed, and a method for producing the same.
2. Description of the Related Art
In compliance with the recent trend of making chip components compact and lightweight, circuit boards for packaging these components are also required to be compact and lightweight. A glass-ceramic multilayer circuit board is effective for responding to the requirements described above because a highly integrated wiring is made possible with the glass-ceramic multilayer circuit board while making the board thin. However, such glass-ceramic multilayer circuit boards are produced through a baking step and usually accompanied by contraction during the sintering process so that a dimensional distribution of, for example, about xc2x10.5% is inevitable using the currently available technology. Such dimensional distribution becomes more evident in a glass-ceramic multilayer board having a cavity for housing appropriate electronic components.
Japanese Unexamined Patent Publication No. 5-102666 or Japanese Unexamined Patent Publication No. 7-330445 proposes, for example, a method for producing a glass-ceramic multilayer circuit board with a high dimensional precision, and Japanese Unexamined Patent Publication No. 6-329476 proposes, for example, a method for producing a glass-ceramic multilayer circuit board having a cavity, wherein green sheets which are not sintered at the sintering temperature of a glass-ceramic molded body are laminated on one side or on both sides of the glass-ceramic molded body and, after baking the green sheet in the laminated state, powder layers originating from such green sheet are removed.
However, according to the method for producing the glass-ceramic multilayer circuit board as described above, a complicated process is required for removing the powder layers originating from the green sheet after baking, and it becomes impossible to previously form a conductive layer on the surface of the glass-ceramic molded body before baking in order to bake the conductive layer simultaneously with the glass-ceramic molded body. Another problem is that surface roughness of the glass-ceramic multilayer circuit board after removing the powder layer originating from the green sheet becomes large.
Japanese Unexamined Patent Publication No. 9-266363 discloses a method comprising the step of sintering merely the glass-ceramic layer by baking the glass-ceramic layer in a laminated state with an alumina layer, allowing the glass component contained in the glass-ceramic layer to permeate into the alumina layer while the alumina layer remains to be non-sintered state, thereby allowing the alumina layer to be solidified. In this case, the glass permeating from the glass-ceramic layer is never distributed throughout the entire area of the alumina layer, but instead the surface is polished simultaneously with removing the non-solidified portion of the alumina layer and a conductive film for the circuit pattern is formed after the foregoing removing and polishing steps.
Accordingly, while it is possible to diminish surface roughness by the removing and polishing steps according to the conventional art, an independent removing step after the baking step as in the foregoing conventional art is also required, making it impossible to obtain the conductive film to be formed on the surface of the circuit board by baking the film simultaneously with the glass-ceramic layer.
Japanese Unexamined Patent Publication No. 5-136572 discloses a method, as in the foregoing conventional art, comprising the step of laminating green sheets that are not sintered at the baking temperature of the glass-ceramic on one face or on both faces of the glass-ceramic molded body, followed by sintering merely the glass-ceramic molded body. In this method, the powder layer originating from the non-sintered green sheet is filled with a resin.
According to the conventional arts, a separate step of filling the resin is required, although the step of removing the non-sintered powder layer has been excluded.
Accordingly, the object of the present invention is to provide a laminated body that does not especially require post-treatment steps such as a removing step and resin filling step after the baking step to attain a state that can be offered for use, and a method for producing the same.
One preferred embodiment of the present invention provides a laminated body, comprising:
a first sheet layer comprising an aggregate of a first powder, at least a part of the first powder being in a sintered state;
a second sheet layer disposed so as to make a contact with the first sheet layer and comprising an aggregate of a second powder, the second powder being in a non-sintered state; and
the first powder and the second powder being solidified to each other by allowing a part of the first sheet layer material to diffuse or to flow into the second sheet layer.
In the above described laminated body, the part of the first sheet layer material may diffuse or flow into the entire area of the second sheet layer and the overall second powder is solidified with the first sheet layer material.
In the above described laminated body, at least a part of the first powder may have a melting point lower than the sintering temperature of the second powder.
In the above described laminated body, the aggregate of the first powder may contain a glass material.
In the above described laminated body, the glass material may comprise a material made to be a glassy state by melting through baking.
In the above described laminated body, the glass material may comprise a nucleated glass material.
In the above described laminated body, the aggregate of the first powder may further comprise a ceramic material.
In the above described laminated body, the aggregate of the first powder may comprise a mixed material comprising at least one of anorthite nucleated glass, borosilicate glass and corgelite system nucleated glass and alumina.
In the above described laminated body, the aggregate of the second powder may comprise a ceramic material.
In the above described laminated body, a plurality of the first sheet layers may be laminated via the second sheet layer.
In the above described laminated body, a pair of the first sheet layers respectively positioned at each side of the second sheet layer may have substantially the same thickness with each other.
In the above described laminated body, a plurality of the second sheet layers may be laminated via the first sheet layer.
In the above described laminated body, a conductive film may be provided on the surface and/or inside of the laminated body, so that thereby the first sheet layers, the second sheet layers and the conductive film constitute a circuit board.
In the above described laminated body, the second sheet layer may be thinner than the first sheet layer.
In the above described laminated body, a cavity may be provided so as to allow its opening to be positioned along at least one of the principal faces of the laminated body.
Another preferred embodiment of the present invention further provides a method for producing a laminated body comprising the steps of:
a first step for preparing a raw laminated body provided with a first sheet layer being in a raw state comprising a first powder and a second sheet layer being in a raw state disposed so as to make contact with the first sheet layer and comprising a second powder not sintered at a temperature capable of sintering at least a part of the first powder; and
a second step for baking the raw laminated body at a predetermined temperature so as to allow at least a part of the first powder to be sintered and the second powder to be not sintered, along with solidifying the first sheet layer and the second sheet layer to each other by allowing a part of the first sheet layer material to diffuse or to flow into the second sheet layer.
In the above described method, the raw laminated body may comprise a plurality of the first sheet layers laminated via the second sheet layer, and a pair of the first sheet layers respectively positioned at each side of the second sheet layer may have substantially the same thickness with each other.
In the above described method, the first sheet layer may be prepared as a first green sheet comprising the first powder in the first step.
In the above described method, the second sheet layer may be prepared as a second green sheet comprising the second powder in the first step, the first step including a step for laminating the second green sheet so as to make contact with the first green sheet.
In the above described method, a sheet composition obtained by forming the second sheet layer on the first green sheet may be prepared in the first step, at least a part of the raw laminated body comprising the sheet composition.
In the above described method, the first sheet layer may comprise a portion obtained by laminating a plurality of the first green sheets so as to make contact with each other at least a part of the first sheet layer in the first step.
In the above described method, a part of the first sheet layer may diffuse or flow into the entire area of the second sheet layer to solidify the overall second powder in the second step.
In the above described method, the first step may include a step for forming the conductive film on the surface and/or inside of the raw laminated body.
In the above described method, the conductive film may contain a conductive metal powder that is sintered in the second step.
In the above described method, the second sheet layer may be thinner than the first sheet layer in the raw laminated body.
In the above described method, the first step may include a step for forming a cavity so as to allow its opening to be positioned along at least one of the principal faces of the raw laminated body.
In the above described method, the first step may include a step for laminating a plurality of the green sheets to obtain the raw laminated body, and the step for forming the cavity may include a step for disposing a penetrating hole through a specified green sheet positioned at outside among the plural green sheets.
In the above described method, the step for providing the penetrating hole may be executed prior to the step for laminating a plurality of the green sheets.
In the above described method, the lamination step may include a pre-lamination step for obtaining a pre-laminating body by previously laminating the layers to be provided with the penetrating hole among the plural green sheets to be laminated, and the step for providing the penetrating hole may include the step for providing a penetrating hole through the pre-laminating body.
As described above, the present invention provides a laminated body provided with first sheet layers and second sheet layers disposed to make contact with the first sheet layers, wherein at least a part of a first powder contained in the first sheet layer is in a sintered state while a second powder contained in the second sheet layer is in a non-sintered state. However, the laminated body itself can be offered for use without removing the second sheet layer after processing or without applying any treatment for filling the composition with a resin because the second sheet layer is solidified by allowing a part of the first sheet layer to diffuse or flow into the second sheet layer.
Excluding the need of removing the second sheet layer or filling the resin thereto makes it possible to bake a conductive film formed on the surface simultaneously with baking of the first sheet layer.
Making the particle size of the powder to be contained in the sheet layer positioned on the surface of the laminated body small allows a laminated body with a small surface roughness to be obtained.
Since powders having desired properties such as insulating property, dielectric property, piezoelectric property and magnetic property may be relatively freely used for the second powder contained in the second sheet layer, the laminated body obtained can be easily endowed with specified electromagnetic functions. Production of substrate such as a L-C-R composite substrate may be made easy by an arbitrary combination of these properties. When powders having a high abrasion resistance and high tenacity are used for the second powder, mechanical strength of the laminated body can be enhanced. Otherwise, when powders having light reflection property or infrared light reflection property are used for the second powder, the laminated body can be endowed with a specified optical function.
When the first powder for forming the first sheet layer contains an anorthite nucleated glass powder, such anorthite nucleated glass is easily diffused or flowed into the entire region of the second sheet layer, allowing the overall second powder to be sufficiently solidified with the first powder.
Likewise, when the second sheet layer is thinner than the first sheet layer, a part of the material of the first sheet layer is easy to diffuse or flow into the entire region of the second sheet layer, thereby making it easy to sufficiently solidify the overall second powder with the first sheet layer material.
According to the method for producing the laminated body of the present invention, the second powder is especially not sintered in the sintering step, so that the second sheet layer containing this second powder functions so as to suppress contraction of the first sheet layer along the major surface thereof, thereby suppressing contraction of the overall laminated body along the major surface of the first sheet layer due to baking to reduce the dimensional distribution of the laminated body obtained.
Since dimensional distribution is especially liable to occur in a laminated body having a cavity, the present invention can be more advantageously applied to the laminated body having a cavity and the method for producing the same, reducing distortion at the cavity portion when the present invention is applied to the laminated body having a cavity.
When the raw laminated body prepared in the method for producing the laminated body according to the present invention is provided with a pluality of the first sheet layers laminated via the second sheet layer, the degree of contraction of respective first sheet layers in the baking step can be made to be substantially the same with each other provided that the thicknesses of the first sheet layers positioned at each side of the second sheet layer is adjusted to be substantially the same with each other, advantageously suppressing warp in the laminated body after baking.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.